扭转椭圆双折射光纤环形腔输出特性

对扭转椭圆双折射光纤环形腔的带阻输出特性进行了分析和计算。结果表明，任意椭圆偏振态输入，光纤的双折射和扭转使光纤环形腔带阻输出特性中的谐振峰分裂为两组，对应于光纤的两个本征偏振态。谐振频率发生偏移，偏移量取决于光纤的双折射参数和扭转速率，两组谐振峰的相对幅度取决于光纤的双折射参数、扭转速率和输入偏振态。若输入偏振态为双折射光纤本征偏振态之一，就仅出现一组谐振峰。光纤的双折射和扭转对环形腔的精细度没有影响。     

Principal states of polarization for an optical pulse

We propose a generalized definition of principal states of polarization for an optical pulse with arbitrary spectral components. Similar to the principal states defined by Poole et al. (see Electron. Lett. vol. 22, p. 1029, 1986) we show that regardless of the spectral components of the pulse, there exist two orthogonal input states of polarization which minimize/maximize the delay of the pulse. At the output of the fiber, these two principal states of the pulse, although depolarized, are also always orthogonal to each other     

Statistics of the DGD in PMD emulators

We give the statistics of the differential group delay at the output of a polarization-mode dispersion emulator made of a chain of fiber sections with constant birefringence, fixed and arbitrarily selected lengths, and randomly oriented polarization controllers in between.     

Nonlinear polarization coupling and its application to highresolution distributed fiber sensing

A technique for time-resolved, high-resolution distributed pressure sensing utilizing nonlinearly induced birefringence and polarization coupling in optical fibers is proposed. A theory of cross-interaction between two counterpropagating waves which agrees well with numerical simulations is presented. By measuring the relative power of the two principal polarizations of a probe wave at the fiber output, distribution of the linear birefringence along the fiber can be calculated, providing a convenient fiber optic sensor. The proposed sensor uses ultrashort pulses from mode-locked lasers and thus inherently possesses high spatial resolution and simplicity of the sensing head, in addition to the general features shared by all fiber sensors     

对邦加球测量偏振模色散算法的研究

对基于邦加球的偏振模色散 (PMD)测量方法进行了充分的研究 ,利用输出偏振态的随机性 ,提出了一种比较简单而实用的算法 ,利用这种算法 ,对 11km单模光纤和 1 6 7m长保偏光纤进行了测量 ,实验证明这种算法具有很好的实用价值。     

Polarization properties of interferometrically interrogated fiber Bragg grating and tandem-interferometer strain sensors

Lead sensitivity in low-coherence interferometric fiber-optic sensors is a well-known problem. It can lead to a severe degradation in the sensor resolution and accuracy through its effect on the fringe visibility and interferometric phase. These sensitivities have been attributed to birefringence in the various components. In the current work, an analysis of the polarization properties of fiber Bragg grating and tandem-interferometer strain sensors, using Stokes calculus and the Poincare/spl acute/ sphere, is presented. The responses of these sensors as a function of the birefringence properties of the various components under different illuminating conditions are derived. The predicted responses demonstrate very good agreement with experimentally measured responses. These models provide a clear insight into the evolution of the polarization states through the sensor networks. Methods to overcome the lead sensitivity are discussed and demonstrated, which yield a differential strain measurement accuracy of 18 n/spl epsiv//spl middot/rms for a fiber Bragg grating sensor.     

Statistical treatment of the evolution of the principal states ofpolarization in single-mode fibers

A simple relationship is found for the evolution of the principal states of polarization (PSPs) and their differential group delay in fiber links. A simple expression is found, using the relationship, for the probability of the differential group delay (DGD), considering the evolution of the PSPs as a Brownian motion. The theory has been verified experimentally on an optical cable composed of 12 single-mode, shifted-dispersion fibers 2.2-km long. The results show that the DGD grows as the square root of the length when the length of the fiber is far larger than the correlation length of the perturbation. The measured value of DGD can vary substantially in two fibers belonging to the same ensemble, and in the same fiber, considering two frequencies differing by more than 5 nm     

Effect of PDL on the DOP feedback signal in PMD compensation

The impact of polarization dependence loss (PDL) on the degree of polarization (DOP) feedback signal in polarization mode dispersion (PMD) compensation is analyzed. PDL affects DOP only in the presence of PMD, and in the presence of PMD and PDL, DOP relates not only to both PMD and PDL vectors but also to the principal states of polarization (SOPs) components of the output signal; on the other hand, it adds new frequency dependence and is no longer independent of system bit rate. The PDL minimum endangering PMD compensation is determined by the step size of the PMD compensating algorithm and the differential group delay (DGD) value in optical fiber systems. DOP could no longer act as the feedback signal in PMD compensation unless the PDL in the fiber system has been effectively eliminated before PMD compensation.     

Optimization and stabilization of visibility in interferometricfiber-optic sensors using input-polarization control

The effects of input polarization on the output fringe visibility of two-beam interferometric fiber-optic sensors are investigated, and an analysis which predicts the existence of input states of polarization of eigenmodes of the interferometer for which optimum output visibility is obtained is presented. Experimental results obtained using both a bulk-optic and a fiber Mach-Zehnder interferometer are reported that verify this analysis. Active feedback stabilization of the output fringe visibility of an interferometric sensor using automatic input-polarization control is demonstrated     

Analysis of Degree of Polarization as a Control Signal in PMD Compensation Systems Aided by Polarization Scrambling

The performance of degree of polarization (DOP) is investigated as a control signal in polarization-mode dispersion (PMD) compensation systems aided by polarization scrambling. The relation between the input and output polarization states of a signal propagating through a polarization scrambler and a PMD-induced optical fiber is described by a 3 $,times,$3 Stokes transfer matrix. The average DOP of the output signal over a period of polarization scrambling is derived as an alternative to the conventional DOP-based control signal, i.e., minimum DOP. In the presence of first- and all-order PMDs, the performance of the average and minimum DOPs in monitoring of differential group delay (DGD) for different data formats (i.e., RZ and NRZ) is evaluated. The performance of the two control signals are further investigated by calculating the outage probability of a feedforward first-order PMD compensation system. The results show that the average DOP outperforms the minimum DOP and also gives a wider DGD monitoring range.      

Investigation of polarization dispersion in long lengths of single-mode fiber using multilongitudinal mode lasers

We have used multilongitudinal mode lasers to investigate the polarization properties of long lengths of single-mode fiber cable. We find that the individual longitudinal modes are >99-percent polarized after propagation through 54.6 km of cabled fiber; however, the different longitudinal modes have different states of polarization at the output. This difference is caused by polarization dispersion, and we estimate a propagation delay difference for the two principal states of polarization to be 0.42 ps in the 54.6 km of cabled fiber.     

偏振态调谐光纤滤波器的主偏振态分析

应用主偏振态理论,分析了偏振态可调谐物理机制,建立了偏振态可调谐双折射光纤 滤波器理论分析模型,并研究了可调谐滤波器特性与检偏器偏转角、信号偏振态等结构参数之间的关系。研究表明,滤波器调谐特性主要取决于信号光偏振分量相位差,而与信号光偏振矢量幅度、检偏器偏转角无关;适当地选取偏振矢量取向角以及检偏器偏转角,通过合理控制信号光偏振分量相位差,可以使滤波器实现线性等幅调谐。     

An adaptive first-order polarization-mode dispersion compensationsystem aided by polarization scrambling: theory and demonstration

An adaptive polarization-mode dispersion (PMD) compensation system has been developed to cancel the effects of first-order PMD by producing a complementary PMD vector in the receiver. Control parameters for the PMD compensation system comprised of a polarization controller and a PMD emulator are derived from the nonreturn-to-zero (NRZ) signal in the channel to be compensated. Estimates of the link's differential group delay (DGD) and principal states of polarization (PSPs) based on this signal are reliable when the signal power is equally split between the link's two PSP's; however this condition cannot be assumed. To meet this requirement, we scramble the state of polarization (SOP) of the input signal at a rate much greater than the response time of the PMD monitor signal so that each sample represents many different SOP alignments. This approach allows the effective cancellation of the first-order PMD effects within an optical fiber channel     

Optimized spinning design for low PMD fibers: an analyticalapproach

It is known that the differential group delay (DGD) due to polarization mode dispersion (PMD) can be effectively reduced by spinning the fiber during drawing. In this paper, we propose an analytical approach that allows optimization of the spinning design. The fundamental idea is that, in the absence of polarization coupling, an optimized spinning profile can balance the effects of the intrinsic linear birefringence so that the differential group delay can be forced to be periodic and, consequently, have a limited amplitude as a function of distance. Our approach Is independent of the spin profile. In other words, with a fixed set of parameters that characterize a particular spin function, we are able to find analytically the values corresponding to a periodic DGD in a deterministic regime. Numerical results based on waveplate model confirm the analytical prediction and show that PMD can be reduced by about two orders of magnitude with respect to the same fiber without spinning, even after the introduction of random polarization coupling     

Polarization-selective mode coupling in two-mode Hi-Bi fibers

We propose and demonstrate a mode coupler which converts either of the LP₀₁ polarization states in a two-mode high-birefringence (Hi-Bi) fiber to the LP₁₁ mode with the same polarization. We use coupled-mode theory to develop design rules based on the polarization splitting of the beat length between the two lower-order modes. The device can be operated either as a narrow-band device in a region with large intermodal group delay difference or as a broadband device in a region with zero group delay difference. We use this novel device as a key component in a two-mode Hi-Bi fiber polarizer. In this configuration either of the polarization eigenstates can be selected and transmitted with an adjustable extinction ratio which can be as large as 30 dB. The coupling loss in the transmitted state of polarization can be less than 0.2 dB. In the broadband polarizer we demonstrate -20 dB extinction over 42 nm with a potential for considerable improvement. We also propose and experimentally investigate an increased differential group delay obtained by propagating one polarization state in the LP₁₁ mode instead of in the LP₀₁ mode. The largest differential group delay measured in this configuration is 14.5 ps/m which is seven times larger than the differential group delay between the polarization modes. We discuss several possible uses in fiber sensors and measure the transmission of a proposed two-coupler configuration     

偏振模色散和时延抖动对啁啾光纤光栅色散补偿特性的影响

对存在偏振模色散(PMD)和群时延(GD)抖动的非理想线性啁啾光纤光栅的色散补偿特性进行了研究。实验测量了啁啾光纤光栅的群时延谱和偏振模色散光谱，理论分析和实验测量表明，啁啾光纤光栅差分群时延(DGD)抖动与其时延抖动密切相关。通过数值模拟方法，计算了线性啁啾光纤光栅偏振模色散眼图代价与入射到啁啾光纤光栅色散补偿器的光信号的偏振方向的关系，计算结果表明在使用啁啾光纤光栅色散补偿器时应对光信号的偏振方向进行调整，以获得最佳补偿效果。另外结合实验数据，模拟计算并讨论了非理想线性啁啾光纤光栅群时延抖动和偏振模色散引起的信号的展宽和脉冲形状的劣化。     

Depolarization of broadband radiation in optical fibers with the twisted structure of birefringence

The depolarization of broadband linearly polarized radiation that propagates in optical fibers with the twisted structure of birefringence is investigated. The basic relationships for calculating the degree of radiation polarization at the fiber output at arbitrary fiber lengths and arbitrary azimuths of the input linear polarization are obtained. The depolarization length (on the order of several meters) at which the degree of polarization decreases from unity to a certain residual level is found. It is shown that the depolarization length depends on the width of the spectrum of a radiation source, the magnitude of the fiber’s built-in linear birefringence, and the twist pitch. For long fibers (of a length exceeding 50 m), the residual degree of polarization depends on the azimuth of the input linear polarization.     

Polarization mode dispersion in spun fibers with different linearbirefringence and spinning parameters

This paper shows how the initial linear birefringence determines the necessary spinning parameters to produce spun fiber with optimum differential group delay (DGD) and polarization mode dispersion (PMD) properties. DGD measurements are reported on two pairs of fibers, each pair having been fabricated from a particular fiber preform. The fiber pairs each consist of a sample of spun and unspun fiber. These measurements are then compared with theoretical simulations for each fiber to determine the required range of spinning parameters for a given initial linear birefringence. These results should help in optimizing the spinning parameters for producing high-performance spun fibers     

Multi-wavelength fiber laser based on broadband fiber grating and HiBi fiber loop mirror

Multi-wavelength fiber lasers have attracted a lot of in- terest in recent years because of its potential applications in optical wavelength division multiplexing (WDM) systems, fiber sensors, and other fiber-optics instruments. Because of the predominant…     

A Novel Design for Polarization-Independent Single-Pump Fiber-Optic Parametric Amplifiers

We propose a novel scheme for designing fiber-optic parametric amplifiers whose operation does not depend on the input signal polarization. In our scheme, four-wave mixing takes place inside a birefringent fiber pumped at 45deg from a principal axis. We show numerically that output power varies by <0.1 dB for arbitrary states of input polarization under practical conditions